Flexible thermoplastic hose is used in a wide variety of industrial applications. In typical applications, such as food processing, the hose provides a physical conduit interconnecting successive machines in the processing line. The flexible hose is typically coupled to the processing machines by rigid coupling shanks in the form of short tubular sections. In order to obtain an effective seal, the coupling shanks usually have an outer diameter somewhat larger than the inner diameter of the hose.
It is common practice to heat locally the end portions of the hose in order to facilitate their fitting onto the coupling shanks. Heat, properly applied, can soften the thermoplastic material of the hose and render it sufficiently pliable and elastic to fit onto the larger diameter shanks. Typically heat is applied by dipping the end portion of the hose in a container of hot liquid, such as boiling water or heated ethylene glycol. Alternatively, the ends can be heated by manually directing a stream of hot air onto the hose end or subjecting the hose to radiant heat.
None of these heating techniques, however, has proved wholly satisfactory for larger diameter hose having diameters of three inches or more. Dipping in hot liquids, for example, poses a safety hazard due to spillage and splashing and, in addition, introduces potential contaminants into the interior of the hose. The hazard of spillage and splashing arises because of the difficulty in controlling such hose while lowering an end portion into an upright container of hot liquid. The hose is elastic, difficult for a man to bend into short arcs and heavy for a man to handle (a thirty-foot length of eight-inch hose weighs about 225 pounds). Consequently, there is a substantial danger during dipping that the hose will escape from control with consequent spilling, flipping or splashing of boiling hot liquid.
The danger of chemical contamination arises because heated liquids other than water are often used in order to speed up the softening process. In order to reduce the period of time the hose must be held in dipping position, many users employ liquids, such as glycol, having boiling temperatures higher than that of water. Such liquids, however, are necessarily introduced into the interior of the hose where they are potential contaminants to materials passing through the hose. Glycol, for example, would be a poisonous contaminant in food processing hose.
Manual direction of hot air onto the hose is both tiresome and ineffective. It is tiresome because the operator must continuously redirect the hot air source so that it heats all portions of the end in a substantially uniform manner. It is ineffective because the operator is generally unsuccessful in obtaining uniform heating, resulting in a difficult fit and producing localized weak spots in the expanded hose.
Radiant heating is not practical. The surface exposed to radiant heat overheats and begins to smoke and decompose long before the entire thickness is soft enough to expand.